1. Field of the Invention
The present invention relates to a light emitting device, especially to a light emitting device being configured to improve uniformity of luminance of the light emitting device using a point-like light source without depending on the element length of a light guiding body.
2. Description of the Related Art
In recent years, a light emitting device that uses a white light emitting diode (LED) as a light source has been widely applied for the backlight of electronic apparatuses. Since point-like emission of the LED generally has a wide angle distribution, a rod integrator has been conventionally used to configure the LED as a light emitting device having a uniform illumination distribution.
The rod integrator is configured using glass or a transparent resin. Known examples of the rod integrator include a solid rod integrator 100 illustrated in FIG. 4A and a hollow rod integrator 102 illustrated in FIG. 4B. The rod integrator 100 has a light incident surface 100a which is disposed to face LEDs and a light emitting surface 100b that faces the light incident surface 100a. In the solid rod integrator 100, light that has been emitted from the LED is introduced into a solid inner portion through the light incident surface 100a. The light is then adapted to advance toward the light emitting surface 100b while repeating total reflection. Accordingly, the luminance of the light emitting surface 100b can be equalized (see Japanese Patent Application Laid-Open No. 2004-184612).
On the other hand, the hollow rod integrator 102 also has a light incident end 102a which is disposed to face LEDs 104 and a light emitting end 102b that faces the light incident end 102a. In the hollow rod integrator 102, light emitted from the LED 104 is introduced into a hollow inner portion through the light incident end 102a. The light is then adapted to advance toward the light emitting end 102b while repeating total reflection by means of an inner surface 102c. Accordingly, the luminance of an irradiation object (not shown) such as a spatial light modulating device that is arranged in the light emitting end 102b can be equalized (see Japanese Patent Application Laid-Open No. 2006-349987).
Here, the rod integrators 100 and 102 bring light, which has been introduced into the inner portions through the light incident surface 100a and the light incident end 102a, toward the light emitting surface 100b and the light emitting end 102b while totally reflecting the light, thereby achieving the equalization of the luminance. For this reason, in order to obtain the emission of light excellent in uniformity of luminance, it is desired to further extend element length (that is, length in an optical axis direction) of the rod integrators 10, 102. Therefore, like the case of a light guiding plate 106 illustrated in FIG. 5B, when the element length of the light guiding plate 106 is short (that is, the distance between a light incident surface 106a which LEDs 104 face and a light emitting surface 106b facing the light incident surface 106a has not been sufficiently secured), in the luminance of the light emitting surface 106b, as illustrated by a curved line L in FIG. 5A, the level difference of luminance distributions according to the number of LEDs 104 and the arrangement thereof may occur over the entire light emitting surface 106b. 